1. Field of the Invention
The present invention relates to a hand-held power tool, in particular in form of an electrical combination hammer that can be alternatively used as a hammer drill or a chisel hammer and that includes a housing in which there is provided operational means that reciprocates along an operational axis spaced from the gravity center of the tool and extending parallel to a first direction which corresponds to the operational direction of the tool. E.g., the operational means can be formed as a percussion or impact piston of an electro-pneumatic percussion mechanism. The power tool further includes a handle supported on the housing by a spring-mounted decoupling device for preventing transmission of the housing vibrations to the handle. The decoupling device includes a first spring-mounted support and a second spring-mounted support in form of a pivotal support and that is spaced from the operational axis in a second direction, which is perpendicular to the first, operational direction, by a distance greater than the distance the first support is spaced from the operational axis in the second direction.
2. Description of the Prior Art
In hand-held power tools of the type described above, during an operation, the housing is subjected to rotational oscillations which result from the operational axis being spaced from the tool gravity center. The use of a spring-mounted support, which provides for a certain rotation of the handle relative to the tool housing against a biasing force permits to prevent the transmission of the vibrations which act on the housing as a result of rotational oscillations, to the handle. The device permits to reduce vibrations acting on the handle not only in the first operational direction but also in the second direction, increasing the comfort of a user holding the power tool.
The reduction of the vibrations is effected in all directions by a respective, most possible vibration-decoupled suspension of the handle, which quasi-isolates vibrations produced during an operation. Further, dependent on used spring means, more or less large damping effect is achieved. Below, reduction of the vibrations, which does not depend on the portion of the damping effect, for simplicity sake, will be referred to as decoupling.
German Publication DE 33 12 195 A1 discloses a hand-held power tool in form of a rotary-percussion hammer drill with a handle spring-mounted on the tool housing. Between the handle and the housing, there are provided upper spring-mounted means in the region of the percussion or operational axis and lower spring-mounted means that are formed by a spring-supported pivotal support that is spaced from the operational axis. The lower spring-mounted means has a higher spring stiffness than the upper spring-mounted means.
The known decoupling device should insure a stable guidance by the lower spring-mounted means while simultaneously insuring a high damping effect in the percussion or operational direction by the upper spring-mounted means.
However, the drawback of the known hand-held tool consists in that despite the all-side spring action applied to both spring-mounted means, an adequate decoupling of the handle from rotational oscillations acting on the housing is not possible. Rather, because of the rotational oscillations, the spring behavior of both spring-mounted means is superimposed. Because of the relatively stiff lower spring-mounted means and superimposition of the spring action of the upper spring-mounted means in the second direction, during an operation, relatively high vibrations along the second direction still remains.
Accordingly, an object of the present invention is to provide a hand-held power tool in which the drawbacks of the known power tool are eliminated and vibrations which are produced by rotational oscillations and which are transmittable to the handle, are reduced.